U.S. patent number 10,618,036 [Application Number 16/097,488] was granted by the patent office on 2020-04-14 for cobalt catalyst based on a support containing a mixed oxide phase containing cobalt and/or nickel prepared by the use of a dicarboxylic acid comprising at least three carbon atoms.
This patent grant is currently assigned to IFP Energies Nouvelles. The grantee listed for this patent is IFP ENERGIES NOUVELLES. Invention is credited to Dominique Decottignies, Antoine Fecant.
United States Patent |
10,618,036 |
Decottignies , et
al. |
April 14, 2020 |
Cobalt catalyst based on a support containing a mixed oxide phase
containing cobalt and/or nickel prepared by the use of a
dicarboxylic acid comprising at least three carbon atoms
Abstract
The invention concerns a catalyst containing an active cobalt
phase deposited on a support comprising alumina, silica or
silica-alumina, said support containing a mixed oxide phase
containing cobalt and/or nickel, said catalyst being prepared by
introducing at least one dicarboxylic acid comprising at least
three carbon atoms. The invention also concerns its use in the
field of Fischer-Tropsch synthesis processes.
Inventors: |
Decottignies; Dominique
(Saint-Genis-Laval, FR), Fecant; Antoine (Brignais,
FR) |
Applicant: |
Name |
City |
State |
Country |
Type |
IFP ENERGIES NOUVELLES |
Rueil-Malmaison |
N/A |
FR |
|
|
Assignee: |
IFP Energies Nouvelles
(Rueil-Malmaison, FR)
|
Family
ID: |
56943631 |
Appl.
No.: |
16/097,488 |
Filed: |
March 20, 2017 |
PCT
Filed: |
March 20, 2017 |
PCT No.: |
PCT/EP2017/056561 |
371(c)(1),(2),(4) Date: |
October 29, 2018 |
PCT
Pub. No.: |
WO2017/186407 |
PCT
Pub. Date: |
November 02, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190143306 A1 |
May 16, 2019 |
|
Foreign Application Priority Data
|
|
|
|
|
Apr 29, 2016 [FR] |
|
|
16 53851 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J
35/1019 (20130101); B01J 37/0207 (20130101); B01J
37/0203 (20130101); B01J 37/0236 (20130101); B01J
37/08 (20130101); B01J 37/088 (20130101); B01J
21/12 (20130101); B01J 35/1038 (20130101); B01J
23/8913 (20130101); B01J 37/0205 (20130101); C10G
2/50 (20130101); B01J 23/75 (20130101); B01J
35/1042 (20130101); C10G 2/332 (20130101); Y02P
30/20 (20151101) |
Current International
Class: |
B01J
23/75 (20060101); B01J 23/89 (20060101); C10G
2/00 (20060101); B01J 35/10 (20060101); B01J
21/12 (20060101); B01J 37/08 (20060101); B01J
37/02 (20060101) |
Field of
Search: |
;502/524,315,335,337,258-260 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
International Search Report PCT/EP2017/056561 dated Jun. 12, 2017.
(pp. 1-13). cited by applicant.
|
Primary Examiner: Hailey; Patricia L.
Attorney, Agent or Firm: Millen White Zelano & Branigan,
PC
Claims
The invention claimed is:
1. A process for preparing a catalyst containing an active cobalt
phase deposited on a support comprising alumina, silica or
silica-alumina, said support containing a mixed oxide phase
containing cobalt and/or nickel, said process comprising: a)
bringing a support comprising alumina, silica or silica-alumina
into contact with at least one solution containing at least one
precursor of cobalt and/or nickel, then drying and calcining at a
temperature in the range 700.degree. C. to 1200.degree. C., in a
manner such as to obtain a mixed oxide phase containing cobalt
and/or nickel in the support, b) bringing said support containing
said mixed oxide phase into contact with at least one solution
containing at least one precursor of cobalt, c) bringing said
support containing said mixed oxide phase into contact with at
least one dicarboxylic acid comprising at least three carbon atoms,
wherein b) and c) are carried out separately, in any order, or
simultaneously, to form the catalyst, and d) then drying the
catalyst at a temperature of less than 200.degree. C.
2. The process as claimed in claim 1, wherein the mixed oxide phase
content in the support is in the range 0.1% to 50% by weight with
respect to the weight of the support.
3. The process as claimed in claim 1, wherein said support is based
on alumina or silica-alumina and the mixed oxide phase comprises an
aluminate of formula CoAl.sub.2O.sub.4 or formula
NiAl.sub.2O.sub.4.
4. The process as claimed in claim 1, wherein said support is based
on silica or silica-alumina and the mixed oxide phase comprises a
silicate of formula Co.sub.2SiO.sub.4 or formula
Ni.sub.2SiO.sub.4.
5. The process as claimed in claim 1, wherein said support is based
on silica-alumina and the silica content of said support is in the
range 0.5% by weight to 30% by weight with respect to the weight of
the support prior to the formation of the mixed oxide phase.
6. The process as claimed in claim 1, wherein the dicarboxylic acid
comprising at least three carbon atoms introduced during c) is an
aliphatic dicarboxylic acid or aromatic dicarboxylic acid.
7. The process as claimed in claim 6, wherein the dicarboxylic acid
comprising at least three carbon atoms is malonic acid or succinic
acid.
8. The process as claimed in claim 1, wherein the molar ratio of
the dicarboxylic acid comprising at least three carbon atoms
introduced during c) with respect to the elemental cobalt
introduced in b) is in the range 0.01 to 2.0 mol/mol.
9. The process as claimed in claim 1, wherein the elemental cobalt
content introduced as the active phase during b) is in the range 2%
to 40% by weight, expressed as metallic elemental cobalt with
respect to the total weight of the catalyst.
10. The process as claimed in claim 1, wherein the catalyst further
comprises an element selected from the groups VIIIB, IA, IB, IIA,
IIB, IIIA, IIIB and VA, wherein said element is either initially
present on the support before preparation of the catalyst, or is
introduced into the catalyst at any moment during the
preparation.
11. The process as claimed in claim 1, wherein the catalyst further
contains an organic compound other than the dicarboxylic acid
comprising at least three carbon atoms, said organic compound
containing oxygen and/or nitrogen, wherein said organic compound is
either initially present on the support before preparation of the
catalyst, or is introduced into the catalyst at any moment during
the preparation.
12. The process as claimed in claim 11, wherein the organic
compound is selected from a compound comprising one or more
chemical functions selected from a carboxylic, alcohol, ether,
aldehyde, ketone, ester, carbonate, amine, nitrile, imide, oxime,
urea and amide function.
13. The process as claimed in claim 1, wherein, after d), a
calcining e) is carried out at a temperature in the range
200.degree. C. to 550.degree. C., in an inert atmosphere or in an
atmosphere containing oxygen.
14. The process as claimed in claim 13, wherein the catalyst
obtained from m the calcining e) is reduced at a temperature in the
range 200.degree. C. to 500.degree. C.
15. The process as claimed in claim 1, wherein the catalyst
obtained from d) is reduced at a temperature in the range
200.degree. C. to 500.degree. C.
16. The process as claimed in claim 1, wherein the dicarboxylic
acid is an aliphatic dicarboxylic acid.
17. The process as claimed in claim 1, wherein the dicarboxylic
acid is an aromatic dicarboxylic acid.
18. The process as claimed in claim 1, wherein the precursor of
cobalt is in the form of a nitrate, carbonate, acetate, chloride,
or a complex formed with acetylacetonates, and the precursor of
nickel is in the form of a nitrate, carbonate, acetate, chloride,
hydroxide, hydroxycarbonate, oxalate, or a complex formed with
acetylacetonates.
19. The process as claimed in claim 1, wherein the total content of
cobalt and/or nickel is advantageously in the range 1% to 20% by
weight with respect to the weight of the final support.
Description
The invention relates to a catalyst containing an active cobalt
phase deposited on a support comprising alumina, silica or
silica-alumina, said support containing a mixed oxide phase
containing cobalt and/or nickel, said catalyst having been prepared
by introducing at least one dicarboxylic acid comprising at least
three carbon atoms. The invention also relates to its preparation
method and its use in the field of Fischer-Tropsch synthesis
processes.
The present invention relates to the field of Fischer-Tropsch
synthesis processes which can be used to obtain a wide range of
hydrocarbon cuts from a CO+H.sub.2 mixture, which is generally
known as synthesis gas or syngas.
The simplified stoichiometric equation (limited in the equation
below to the formation of alkanes) for the Fischer-Tropsch
synthesis is written as follows:
nCO+(2n+1)H.sub.2.fwdarw.C.sub.nH.sub.2n+2+nH.sub.2O
The catalysts used in the Fischer-Tropsch synthesis are usually
supported catalysts based on alumina, silica or silica-alumina or
combinations of these supports, the active phase principally being
constituted by iron (Fe) or cobalt (Co), optionally doped with a
noble metal such as Pt, Rh or Ru.
Adding an organic compound to Fischer-Tropsch catalysts in order to
improve their activity has been recommended by the person skilled
in the art.
A number of documents describe the use of various ranges of organic
compounds as additives, such as organic compounds containing
nitrogen and/or organic compounds containing oxygen.
In particular, the U.S. Pat. Nos. 5,856,260 and 5,856,261
respectively teach the introduction, during the preparation of the
catalyst, of polyols with general formula CnH.sub.2n+2O.sub.x, in
which n is a whole number in the range 2 to approximately 6, and x
is a whole number in the range 2 to 11 or mono- or disaccharide
type sugars; sucrose is particularly preferred.
Patent application US 2005/0026776 discloses the use of chelating
compounds of the nitrilotriacetic acid (NTA),
trans-1,2-cyclohexadiamine-N,N,N',N' tetraacetic acid (CyDTA) or
ethylenediaminetetraacetic acid (EDTA) type, or in fact glycine,
aspartic acid or citric acid, in order to obtain a catalyst with a
reduced Co.sub.3O.sub.4 crystallite size. Other documents teach the
use of polyethers (WO2014/092278 and WO2015/183061), glyoxylic acid
(WO2015/183059), unsaturated dicarboxylic acids (US2011/0028575) or
in fact multifunctional carboxylic acids with formula
HOOC--(CRR.sup.1).sub.n--COOH in which n.gtoreq.1, in the
preparation of Fischer-Tropsch catalysts (WO98/47618).
The patent application US2014/0353213 describes the use of lactams
or cyclic lactone type esters containing an oxygen atom in the
cycle (.beta.-propiolactone, .gamma.-butyrolactone,
.delta.-valerolactone) or several oxygen atoms in the cycle
(propylene carbonate) in order to increase the activity of an CoMo
or NiMo type catalyst used for hydrodesulphurization of a diesel
type cut.
The document WO2012/013866 discloses the use of a cyclic
oligosaccharide, in particular cyclodextrin, as an additive for a
Fischer-Tropsch catalyst. That document also describes the use of a
support based on silica-alumina optionally containing a spinel.
However, none of the documents pertaining to the additives
describes a catalyst based on cobalt deposited on a support
containing a mixed oxide phase containing cobalt and/or nickel
prepared using a dicarboxylic acid comprising at least three carbon
atoms.
Irrespective of the compounds selected, the modifications induced
could not always sufficiently increase the performances of the
catalyst in order to make the process profitable. In addition,
deploying them on an industrial scale is often very complicated
because they are complex to implement.
As a consequence, it becomes vital for the manufacturers of
catalysts to discover novel catalysts for the Fischer-Tropsch
synthesis which have improved performances.
SUMMARY
The invention provides a catalyst containing an active cobalt phase
deposited on a support comprising alumina, silica or
silica-alumina, said support containing a mixed oxide phase
containing cobalt and/or nickel, said catalyst having been prepared
by a process comprising at least: a) a step for bringing a support
comprising alumina, silica or silica-alumina into contact with at
least one solution containing at least one precursor of cobalt
and/or nickel, then drying and calcining at a temperature in the
range 700.degree. C. to 1200.degree. C., in a manner such as to
obtain a mixed oxide phase containing cobalt and/or nickel in the
support, then carrying out b) a step for bringing said support
containing said mixed oxide phase into contact with at least one
solution containing at least one precursor of cobalt, c) a step for
bringing said support containing said mixed oxide phase into
contact with at least one dicarboxylic acid comprising at least
three carbon atoms, the steps b) and c) possibly being carried out
separately, in any order, or simultaneously, d) then carrying out a
drying step at a temperature of less than 200.degree. C.
The Applicant has in fact established that the use of a
dicarboxylic acid comprising at least three carbon atoms as an
organic additive during the preparation of a catalyst containing an
active cobalt phase deposited on a support comprising alumina,
silica or silica-alumina, said support also containing a mixed
oxide phase containing cobalt and/or nickel, means that a catalyst
for the Fischer-Tropsch synthesis can be obtained which exhibits
improved catalytic performances.
In fact, the catalyst in accordance with the invention exhibits an
increased activity and selectivity compared with catalysts
containing a mixed oxide phase containing cobalt and/or nickel in
their support but prepared without the addition or compared with
catalysts containing additives and containing no mixed oxide phase
which contains cobalt and/or nickel in the support. The use of such
an organic compound during the preparation of a catalyst based on
cobalt containing a support containing a mixed oxide phase which
contains cobalt and/or nickel appears to have a synergistic effect
on the activity and selectivity in a Fischer-Tropsch process.
Without wishing to be bound by a particular theory, it has been
discovered that such a catalyst has a dispersion of cobalt which is
substantially superior to that exhibited by catalysts prepared in
the absence of such an organic compound. It results in the presence
of a larger number of active sites for the catalysts prepared in
the presence of at least one dicarboxylic acid comprising at least
three carbon atoms, even if that compound is subsequently
eliminated at least in part by drying and optional calcining.
In a variation, the mixed oxide phase content in the support is in
the range 0.1% to 50% by weight with respect to the weight of the
support.
In a variation, the mixed oxide phase comprises an aluminate with
formula CoAl.sub.2O.sub.4 or NiAl.sub.2O.sub.4 in the case of a
support based on alumina or silica-alumina.
In a variation, the mixed oxide phase comprises a silicate with
formula Co.sub.2SiO.sub.4 or Ni.sub.2SiO.sub.4 in the case of a
support based on silica or silica-alumina.
In a variation, the silica content of said support is in the range
0.5% by weight to 30% by weight with respect to the weight of the
support prior to the formation of the mixed oxide phase when the
support is a silica-alumina.
In a variation, the dicarboxylic acid comprising at least three
carbon atoms introduced during step c) is selected from an
aliphatic or aromatic dicarboxylic acid.
In accordance with this variation, the dicarboxylic acid comprising
at least three carbon atoms is selected from malonic acid or
succinic acid.
In a variation, the molar ratio of the dicarboxylic acid comprising
at least three carbon atoms introduced during step c) with respect
to the elemental cobalt introduced in step b) is in the range 0.01
to 2.0 mol/mol.
In a variation, the elemental cobalt content introduced as the
active phase during step b) is in the range 2% to 40% by weight,
expressed as metallic elemental cobalt with respect to the total
weight of the catalyst.
In a variation, the catalyst further comprises an element selected
from the groups VIIIB, IA, IB, IIA, IIB, IIIA, IIIB and VA.
In a variation, the catalyst further contains an organic compound
other than the dicarboxylic acid comprising at least three carbon
atoms, said organic compound containing oxygen and/or nitrogen.
In a variation, the organic compound is selected from a compound
comprising one or more chemical functions selected from a
carboxylic, alcohol, ether, aldehyde, ketone, ester, carbonate,
amine, nitrile, imide, oxime, urea and amide function.
In a variation, after the drying step d), a calcining step e) is
carried out at a temperature in the range 200.degree. C. to
550.degree. C., in an inert atmosphere or in an atmosphere
containing oxygen.
In a variation, the catalyst obtained from the drying step d) or
obtained from the calcining step e) is reduced at a temperature in
the range 200.degree. C. to 500.degree. C.
The invention also concerns the use of the catalyst in accordance
with the invention in a Fischer-Tropsch synthesis process, in which
the catalyst in accordance with the invention is brought into
contact with a feed comprising synthesis gas at a total pressure in
the range 0.1 to 15 MPa, at a temperature in the range 150.degree.
C. to 350.degree. C., and at an hourly space velocity in the range
100 to 20000 volumes of synthesis gas per volume of catalyst and
per hour, with a molar ratio H.sub.2/CO in the synthesis gas in the
range 0.5 to 4.
Hereinbelow, the groups of chemical elements are given in
accordance with the CAS classification (CRC Handbook of Chemistry
and Physics, published by CRC Press, Editor-in-Chief D. R. Lide,
81.sup.st edition, 2000-2001). As an example, group VIII in the CAS
classification corresponds to metals from columns 8, 9 and 10 of
the new IUPAC classification.
The textural and structural properties of the support and the
catalyst described hereinbelow are determined using
characterization methods known to the person skilled in the art.
The total pore volume and the pore distribution are determined in
the present invention by nitrogen porosimetry, as described in the
work "Adsorption by powders and porous solids. Principles,
methodology and applications" written by F. Rouquerol, J. Rouquerol
and K. Sing, Academic Press, 1999.
The term "specific surface area" means the BET specific surface
area (S.sub.BET in m.sup.2/g) determined by nitrogen adsorption in
accordance with the ASTM standard D 3663-78 which was established
from the BRUNAUER-EMMETT-TELLER method described in the periodical
"The Journal of American Society", 1938, 60, 309.
DETAILED DESCRIPTION OF THE INVENTION
The catalyst in accordance with the invention is a catalyst
containing an active cobalt phase deposited on a support comprising
alumina, silica or silica-alumina, said support containing a mixed
oxide phase containing cobalt and/or nickel, said catalyst having
been prepared by a process comprising at least: a) a step for
bringing a support comprising alumina, silica or silica-alumina
into contact with at least one solution containing at least one
precursor of cobalt and/or nickel, then drying and calcining at a
temperature in the range 700.degree. C. to 1200.degree. C., in a
manner such as to obtain a mixed oxide phase containing cobalt
and/or nickel in the support, then carrying out b) a step for
bringing said support containing said mixed oxide phase into
contact with at least one solution containing at least one
precursor of cobalt, c) a step for bringing said support containing
said mixed oxide phase into contact with at least one dicarboxylic
acid comprising at least three carbon atoms, the steps b) and c)
possibly being carried out separately, in any order, or
simultaneously, d) then carrying out a drying step at a temperature
of less than 200.degree. C.
The various steps of the process leading to the catalyst in
accordance with the invention will be described in detail
below:
Step a) Formation of the Mixed Oxide Phase Containing Cobalt and/or
Nickel
The aim of step a) is the formation of a mixed oxide phase
containing cobalt and/or nickel in a support comprising alumina,
silica or silica-alumina, by contact with a solution containing at
least one precursor of cobalt and/or nickel, followed by drying and
calcining at high temperature.
It is known that the presence of a mixed oxide phase containing
cobalt and/or nickel in a support of the alumina, silica or
silica-alumina type means that resistance to the phenomenon of
chemical and mechanical attrition in a Fischer-Tropsch process can
be improved, and thus the support can be stabilized.
The formation of the mixed oxide phase in the support, often termed
the support stabilizing step, may be carried out using any method
known to the person skilled in the art. It is generally carried out
by introducing the cobalt and/or nickel in the form of a precursor
of a salt, for example of the nitrate type, onto the initial
support containing alumina, silica or silica-alumina. By calcining
the mixed oxide phase containing cobalt and/or nickel at very high
temperatures, the support as a whole is formed and stabilized. The
cobalt and/or nickel contained in the mixed oxide phase cannot be
reduced during final activation of the Fischer-Tropsch catalyst
(reduction). The cobalt and/or nickel contained in the mixed oxide
phase thus does not constitute the active phase of the
catalyst.
In accordance with step a), a step is carried out for bringing a
support comprising alumina, silica or silica-alumina into contact
with at least one solution containing at least one precursor of
cobalt and/or nickel, then drying and calcining at a temperature in
the range 700.degree. C. to 1200.degree. C., in a manner such as to
obtain a mixed oxide phase containing cobalt and/or nickel in the
support.
More particularly, the contact step a) may be carried out by
impregnation, preferably dry impregnation, of a support comprising
alumina, silica or silica-alumina, pre-formed or as a powder, with
at least one aqueous solution containing the precursor of cobalt
and/or nickel, followed by drying and calcining at a temperature in
the range 700.degree. C. to 1200.degree. C.
The cobalt is brought into contact with the support via any
precursor of cobalt which is soluble in an aqueous phase.
Preferably, the precursor of cobalt is introduced in aqueous
solution, preferably in the form of the nitrate, carbonate,
acetate, chloride, complexes formed with acetylacetonates, or any
other inorganic derivative which is soluble in aqueous solution
which is brought into contact with said support. The cobalt
precursor which is advantageously used is cobalt nitrate or cobalt
acetate.
The nickel is brought into contact with the support via any
precursor of nickel which is soluble in an aqueous phase.
Preferably, said precursor of nickel is introduced in aqueous
solution, for example in the form of the nitrate, carbonate,
acetate, chloride, hydroxide, hydroxycarbonate, oxalate, complexes
formed with acetylacetonates, or any other inorganic derivative
which is soluble in aqueous solution which is brought into contact
with said support. The precursor of nickel which is advantageously
used is nickel nitrate, nickel chloride, nickel acetate or nickel
hydroxycarbonate.
The total content of cobalt and/or nickel is advantageously in the
range 1% to 20% by weight and preferably in the range 2% to 10% by
weight with respect to the weight of the final support.
Drying is advantageously carried out at a temperature in the range
60.degree. C. to 200.degree. C., preferably for a period of 30
minutes to three hours.
Calcining is carried out at a temperature in the range 700.degree.
C. to 1200.degree. C., preferably in the range 850.degree. C. to
1200.degree. C., and more preferably in the range 850.degree. C. to
900.degree. C., generally for a period in the range from one hour
to 24 hours and preferably in the range 2 hours to 5 hours. The
calcining is generally carried out in an oxidizing atmosphere, for
example in air, or in air depleted in oxygen; it may also be
carried out at least in part under nitrogen. It can be used to
transform the cobalt and/or nickel precursors and alumina and/or
silica into a mixed oxide phase containing cobalt and/or
nickel.
In accordance with a variation, calcining may also be carried out
in two steps, said calcining advantageously being carried out at a
temperature in the range 300.degree. C. to 600.degree. C. in air
for a period in the range from half an hour to three hours, then at
a temperature in the range 700.degree. C. to 1200.degree. C.,
preferably in the range 850.degree. C. to 1200.degree. C. and more
preferably in the range 850.degree. C. to 900.degree. C., generally
for a period in the range from one hour to 24 hours, and preferably
in the range 2 hours to 5 hours.
The support comprises alumina, silica or silica-alumina.
When the support comprises alumina, it contains more than 50% by
weight of alumina with respect to the weight of the support before
the formation of the mixed oxide phase, and preferably it contains
only alumina. The alumina may be present in a crystallographic
gamma, delta, theta, or alpha form, alone or as a mixture.
In another preferred case, the support comprises silica. In this
case, it contains more than 50% by weight of silica with respect to
the weight of the support before the formation of the mixed oxide
phase, and preferably it contains silica alone. The sources of
silica are well known to the person skilled in the art.
In another preferred case, the support comprises a silica-alumina.
The term "support comprising a silica-alumina" means a support in
which the silicon and aluminium are in the form of agglomerates of
silica or alumina respectively, amorphous aluminosilicate or any
other mixed phase containing silicon and aluminium, it being
understood that the support is not mesostructured. Preferably, the
alumina and the silica are present in the form of a mixture of
SiO.sub.2 and Al.sub.2O.sub.3 oxides. The silica content in the
silica-alumina support varies from 0.5% by weight to 30% by weight,
preferably from 1% by weight to 25% by weight, and more preferably
from 1.5% to 20% by weight with respect to the weight of the
support before the formation of the mixed oxide phase.
In accordance with a preferred variation, the support is
constituted by alumina, silica or silica-alumina, and particularly
preferably the support is constituted by silica-alumina.
The support also contains a mixed oxide phase containing cobalt
and/or nickel. The term "mixed oxide phase containing cobalt and/or
nickel" should be understood to mean a phase in which cobalt and/or
nickel cations are combined with oxide ions O.sup.2- of the alumina
and/or silica support, thereby forming a mixed phase containing
aluminates and/or silicates containing cobalt and/or nickel. The
mixed oxide phase may be in the amorphous form or in the
crystalline form.
When the support is based on alumina, the mixed oxide phase may
comprise an aluminate with formula CoAl.sub.2O.sub.4 or
NiAl.sub.2O.sub.4, in the amorphous or crystalline form, for
example in the form of spinel.
When the support is based on silica, the mixed oxide phase may
comprise a silicate with formula Co.sub.2SiO.sub.4 or
Ni.sub.2SiO.sub.4 (cobalt or nickel orthosilicate), in the
amorphous or crystalline form.
When the support is based on silica-alumina, the mixed oxide phase
may comprise an aluminate with formula CoAl.sub.2O.sub.4 or
NiAl.sub.2O.sub.4 in the amorphous or crystalline form, for example
in the form of spinel, and/or a silicate with formula
Co.sub.2SiO.sub.4 or Ni.sub.2SiO.sub.4, in the amorphous or
crystalline form.
In general, the content of the mixed oxide phase in the support is
in the range 0.1% to 50% by weight with respect to the weight of
the support, preferably in the range 0.5% to 30% by weight, and
more preferably in the range 1% to 20% by weight.
The presence of a mixed oxide phase in the catalyst in accordance
with the invention is measured by temperature programmed reduction
(TPR) as described, for example, in Oil & Gas Science and
Technology, Rev. IFP, Vol. 64 (2009), No. 1, pp. 11-12. In that
technique, the catalyst is heated in a stream of a reducing agent,
for example in a stream of dihydrogen. The measurement of the
dihydrogen consumed as a function of the temperature provides
quantitative information regarding the reducibility of the species
present. The presence of a mixed oxide phase in the catalyst is
then demonstrated by a consumption of dihydrogen at a temperature
of more than approximately 800.degree. C.
The support may have a morphology in the form of beads, extrudates
(for example in the form of trilobes or quadrilobes) or pellets, in
particular when said catalyst is employed in a reactor functioning
in fixed bed mode, or it may have a powder type morphology with a
variable granulometry, in particular when said catalyst is employed
in a reactor of the slurry bubble column type. The grain size of
the catalyst may be in the range from a few microns to a few
hundred microns. When operating in a slurry type reactor, the grain
size of the catalyst is preferably in the range 10 microns to 500
microns, preferably in the range 10 microns to 300 microns, highly
preferably in the range 20 to 200 microns, and yet more preferably
in the range 30 to 160 microns.
The specific surface area of the support containing the mixed oxide
phase is generally in the range 50 m.sup.2/g to 500 m.sup.2/g,
preferably in the range 100 m.sup.2/g to 300 m.sup.2/g, more
preferably in the range 150 m.sup.2/g to 250.sup.2/g. The pore
volume of said support is generally in the range 0.3 mL/g to 1.2
mL/g, and preferably in the range 0.4 mL/g to 1 mL/g.
Thus, at the end of said step a), said support comprising alumina,
silica or silica-alumina further comprises a mixed oxide phase
containing cobalt and/or nickel.
Step b) and c): Introduction of the Active Phase and of the
Dicarboxylic Acid Comprising at Least Three Carbon Atoms
Following the formation of the mixed oxide phase, the following
steps are carried out in the preparation of the catalyst in
accordance with the invention: b) a step for bringing said support
containing said mixed oxide phase into contact with at least one
solution containing at least one precursor of cobalt, c) a step for
bringing said support containing said mixed oxide phase into
contact with at least one dicarboxylic acid comprising at least
three carbon atoms, the steps b) and c) possibly being carried out
separately, in any order, or simultaneously.
Step b) for bringing said support into contact with at least one
solution containing at least one precursor of cobalt may be carried
out using any method which is well known to the person skilled in
the art. Said step b) is preferably carried out by impregnation of
the support with at least one solution containing at least one
precursor of cobalt. In particular, said step b) may be carried out
by dry impregnation, by excess impregnation, or by
deposition--precipitation (as described in U.S. Pat. Nos. 5,874,381
and 6,534,436) in accordance with methods which are well known to
the person skilled in the art. Preferably, said step b) is carried
out by dry impregnation, which consists of bringing the catalyst
support into contact with a solution containing at least one
precursor of cobalt, the volume of which is equal to the pore
volume of the support to be impregnated. This solution contains the
cobalt precursor at the desired concentration.
The cobalt is brought into contact with said support by means of
any precursor of cobalt which is soluble in an aqueous phase or in
an organic phase. When it is introduced in organic solution, said
precursor of cobalt is cobalt acetate, for example. Preferably,
said precursor of cobalt is introduced in aqueous solution, for
example in the form of the nitrate, carbonate, acetate, chloride,
complexes formed with acetylacetonates, or any other inorganic
derivative which is soluble in aqueous solution, which is brought
into contact with said support. Advantageously, cobalt nitrate or
cobalt acetate is used as the precursor of cobalt.
The cobalt element content is in the range 2% to 40% by weight,
preferably in the range 5% to 30% by weight, and more preferably in
the range 10% to 25% by weight, expressed as the metallic cobalt
element with respect to the total weight of the catalyst.
The catalyst may advantageously further comprise at least one
element selected from an element from groups VIIIB, IA, IB, IIA,
IIB, IIIA, IIIB and/or VA.
Preferred optional elements from group VIIIB are platinum,
ruthenium and rhodium. The preferred elements from group IA are
sodium and potassium. The preferred elements from group IB are
silver and gold. The preferred elements from group IIA are
manganese and calcium. The preferred element from group IIB is
zinc. The preferred elements from group IIIA are boron and indium.
The preferred elements from group IIIB are lanthanum and cerium.
The preferred element from group VI is phosphorus.
The content of the optional element from groups VIIIB, IA, IB, IIA,
IIB, IIIA, IIIB and/or VA is in the range 50 ppm to 20% by weight,
preferably in the range 100 ppm to 15% by weight, and more
preferably in the range 100 ppm to 10% by weight, expressed as the
element with respect to the total weight of the catalyst.
In a variation, when the catalyst contains one or more supplemental
elements from groups VIIIB, IA, IB, IIA, IIB, IIIA, IIIB and/or VA,
this element or these elements may either be initially present on
the support before the preparation of the catalyst, or are
introduced at any moment during the preparation and by using any of
the methods known to the person skilled in the art.
Contact of the organic compound employed in order to carry out said
step c) with said support is carried out by impregnation, in
particular by dry impregnation or excess impregnation, preferably
by dry impregnation. Said organic compound is preferably
impregnated onto said support after dissolving it in aqueous
solution.
Said dicarboxylic acid comprising at least three carbon atoms may
be selected from aliphatic or aromatic dicarboxylic acids.
In the case of aliphatic dicarboxylic acids, the compound may be a
saturated dicarboxylic acid such as malonic acid, succinic acid or
glutaric acid, or an unsaturated dicarboxylic acid such as maleic
acid or fumaric acid. Preferably, the aliphatic dicarboxylic acid
is a saturated dicarboxylic acid.
In the case of aromatic dicarboxylic acids, the compound may be
phthalic acid, isophthalic acid or terephthalic acid.
The molar ratio of the dicarboxylic acid comprising at least three
carbon atoms introduced during step c) with respect to the
elemental cobalt introduced in step b) is in the range 0.01 to 2.0
mol/mol, preferably in the range 0.05 to 1.0.
In addition to the dicarboxylic acid comprising at least three
carbon atoms, the catalyst in accordance with the invention may
comprise another organic compound or a group of organic compounds
which are known to act as additives. The function of additives is
to increase the catalytic activity compared with catalysts without
additives. More particularly, the catalyst in accordance with the
invention may also comprise one or more organic compounds
containing oxygen and/or nitrogen.
In general, the organic compound is selected from a compound
comprising one or more chemical functions selected from a
carboxylic, alcohol, ether, aldehyde, ketone, ester, carbonate,
amine, nitrile, imide, oxime, urea and amide function.
The organic compound containing oxygen may be one or more selected
from compounds comprising one or more chemical functions selected
from a carboxylic, alcohol, ether, aldehyde, ketone, ester or
carbonate function. By way of example, the organic compound
containing oxygen may be one or more selected from the group
constituted by ethyleneglycol, diethyleneglycol, triethyleneglycol,
a polyethyleneglycol (with a molecular weight in the range 200 to
1500 g/mol), propyleneglycol, 2-butoxyethanol,
2-(2-butoxyethoxy)ethanol, 2-(2-methoxyethoxy)ethanol,
triethyleneglycol dimethylether, glycerol, acetophenone,
2,4-pentanedione, pentanone, acetic acid, malic acid, oxalic acid,
gluconic acid, tartaric acid, citric acid, succinic acid,
.gamma.-ketovaleric acid, .gamma.-valerolactone, 4-hydroxyvaleric
acid, 2-pentenoic acid, 3-pentenoic acid, 4-pentenoic acid, a C1-C4
dialkyl succinate, methyl acetoacetate, dibenzofuran, a crown
ether, orthophthalic acid, glucose and propylene carbonate.
The organic compound containing nitrogen may be one or more
selected from compounds comprising one or more chemical functions
selected from an amine or nitrile function. By way of example, the
organic compound containing nitrogen may be one or more selected
from the group constituted by ethylenediamine, diethylenetriamine,
hexamethylenediamine, triethylenetetramine, tetraethylenepentamine,
pentaethylenehexamine, acetonitrile, octylamine, guanidine or a
carbazole.
The organic compound containing oxygen and nitrogen may be one or
more selected from compounds comprising one or more chemical
functions selected from a carboxylic, alcohol, ether, aldehyde,
ketone, ester, carbonate, amine, nitrile, imide, oxime, urea and
amide function. By way of example, the organic compound containing
oxygen and nitrogen may be one or more selected from the group
constituted by 1,2-cyclohexanediaminetetraacetic acid,
monoethanolamine (MEA), N-methylpyrrolidone, dimethylformamide,
ethylenediaminetetraacetic acid (EDTA), alanine, glycine,
nitrilotriacetic acid (NTA),
N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid (HEDTA),
diethylene-triaminepentaacetic acid (DTPA), tetramethylurea,
glutamic acid, dimethylglyoxime, bicine or tricine, or indeed a
lactam.
The total molar ratio of organic compound(s) containing oxygen
and/or nitrogen other than the dicarboxylic acid comprising at
least three carbon atoms with respect to the elemental cobalt
introduced in step b) is in the range 0.01 to 2 mol/mol, preferably
in the range 0.1 to 2 mol/mol, more preferably in the range 0.2 to
1.5 mol/mol, calculated on the basis of the components introduced
into the impregnation solution(s).
When the catalyst further contains an organic compound other than
the dicarboxylic acid comprising at least three carbon atoms, this
organic compound may either be initially present on the support
before the preparation of the catalyst, or incorporated into the
catalyst at any time during the preparation and using any of the
methods known to the person skilled in the art.
Carrying Out Steps b) and c)
The process for the preparation of the catalyst in accordance with
the invention, in particular steps b) and c), comprises several
embodiments. They are in particular distinguished by the time at
which the organic compound is introduced; it may be either at the
same time as the impregnation of the cobalt of the active phase
(co-impregnation), or after impregnation of the cobalt of the
active phase (post-impregnation), or before impregnation of the
cobalt of the active phase (pre-impregnation). In addition, the
embodiments may be combined.
A first embodiment consists of carrying out said steps b) and c)
simultaneously in a manner such that said organic compound and at
least said cobalt precursor present in the active phase are
co-impregnated onto said support (co-impregnation). Said first
embodiment advantageously comprises carrying out one or more steps
b). In particular, one or more steps b) advantageously precede
and/or follow said co-impregnation step. Said first embodiment may
comprise several co-impregnation steps.
A second embodiment consists of carrying out said step b) prior to
said step c) (post-impregnation). In accordance with said second
embodiment, one or more steps b) for contact of at least cobalt
present in the active phase of the catalyst precede(s) said step
c).
A third embodiment consists of carrying out said step c) prior to
said step b) (pre-impregnation). Advantageously, said step c) is
followed by several steps b).
When the steps b) and c) are carried out separately
(post-impregnation or pre-impregnation), a drying step is
advantageously carried out between the impregnation steps. The
intermediate drying step is carried out at a temperature of less
than 200.degree. C., advantageously in the range 50.degree. C. to
180.degree. C., preferably in the range 70.degree. C. to
150.degree. C., more preferably in the range 75.degree. C. to
130.degree. C., and optionally, a maturation period is carried out
between the impregnation step and the intermediate drying step.
Each of the three embodiments described above may be carried out
independently in a manner such that the catalyst in accordance with
the invention is prepared either in accordance with said first
embodiment, or in accordance with said second embodiment, or in
fact in accordance with said third embodiment. However, it may be
advantageous to combine said first embodiment with said second
embodiment or with said third embodiment: deposition of the cobalt
present in the active phase as well as the organic compound onto
the catalyst support is carried out at least twice, namely at least
once by co-impregnation and at least once by successive
impregnation.
Advantageously, after each impregnation step, irrespective of
whether it is a step for the impregnation of cobalt or organic
compound, the impregnated support is allowed to mature. Maturation
can allow the impregnation solution to become homogeneously
dispersed within the support.
Any maturation step described in the present invention is
advantageously carried out at atmospheric pressure, in an
atmosphere saturated with water and at a temperature in the range
17.degree. C. to 50.degree. C., and preferably at ambient
temperature. Generally, a maturation period in the range from ten
minutes to forty-eight hours and preferably in the range from
thirty minutes to five hours is sufficient. Longer periods are not
excluded, but do not necessary provide any improvement.
Any impregnation solution described in the present invention may
include any polar solvent known to the person skilled in the art.
Said polar solvent used is advantageously selected from the group
formed by methanol, ethanol, water, phenol and cyclohexanol, used
alone or as a mixture. Said polar solvent may also be selected from
the group formed by propylene carbonate, DMSO (dimethylsulphoxide),
N-methylpyrrolidone (NMP) or sulpholane, used alone or as a
mixture. Preferably, a polar protic solvent is used. A list of the
usual polar solvents as well as their dielectric constants can be
found in the book "Solvents and Solvent Effects in Organic
Chemistry" C. Reichardt, Wiley-VCH, third edition, 2003, pages
472-474. Highly preferably, the solvent used is water or ethanol,
and particularly preferably, the solvent is water. In one possible
embodiment, the solvent may be absent from the impregnation
solution.
When several impregnation steps are carried out, each impregnation
step is preferably followed by an intermediate drying step at a
temperature of less than 200.degree. C., advantageously in the
range 50.degree. C. to 180.degree. C., preferably in the range
70.degree. C. to 150.degree. C., highly preferably in the range
75.degree. C. to 130.degree. C., and optionally, a maturation
period is carried out between the impregnation step and the
intermediate drying step.
Drying Step d)
In accordance with the drying step d) when carrying out the
preparation of the catalyst prepared in accordance with at least
one embodiment as described above, drying is carried out at a
temperature of less than 200.degree. C., advantageously in the
range 50.degree. C. to 180.degree. C., preferably in the range
70.degree. C. to 150.degree. C., highly preferably in the range
75.degree. C. to 130.degree. C. The drying step is preferably
carried out over a period in the range 1 to 4 hours, preferably in
an inert atmosphere or in an atmosphere containing oxygen.
The drying step may be carried out using any technique which is
known to the person skilled in the art. It is advantageously
carried out at atmospheric pressure or under reduced pressure.
Preferably, this step is carried out at atmospheric pressure. It is
advantageously carried out in a flushed bed using air or any other
hot gas. Preferably, when drying is carried out in a fixed bed, the
gas used is either air or an inert gas such as argon or nitrogen.
Highly preferably, drying is carried out in a flushed bed in the
presence of nitrogen and/or air. Preferably, the drying step is of
a short duration in the range 5 minutes to 4 hours, preferably in
the range 30 minutes to 4 hours and highly preferably in the range
1 hour to 3 hours.
In accordance with a first variation, drying is preferably carried
out in a manner such as to preserve at least 30% of the
dicarboxylic acid comprising at least three carbon atoms introduced
during an impregnation step; preferably, this quantity is more than
50% and more preferably, more than 70%, calculated on the basis of
the carbon remaining on the catalyst. When an organic compound
containing oxygen and/or nitrogen other than the dicarboxylic acid
comprising at least three carbon atoms is present, the drying step
is preferably carried out in a manner such as to preserve at least
30%, preferably at least 50%, and highly preferably at least 70% of
the quantity introduced, calculated on the basis of the carbon
remaining on the catalyst.
At the end of the drying step d), a dried catalyst is thus obtained
which will undergo an activation step so that it can subsequently
be used in the Fischer-Tropsch synthesis.
In accordance with another variation, at the end of the drying step
d), a calcining step e) is carried out at a temperature in the
range 200.degree. C. to 550.degree. C., preferably in the range
250.degree. C. to 500.degree. C., in an inert atmosphere (for
example nitrogen), or in an atmosphere containing oxygen (for
example air). The duration of this heat treatment is generally in
the range 0.5 hours to 16 hours, preferably in the range 1 hour to
5 hours. After this treatment, the cobalt of the active phase is
then in the oxide form and the catalyst contains no more or very
little of the organic compound introduced during its synthesis.
However, introducing the organic compound during its preparation
has allowed the dispersion of the active phase to be increased,
thereby resulting in a more active and/or more selective
catalyst.
Activation (Reduction)
Prior to using it in the catalytic reactor and carrying out the
Fischer-Tropsch process in accordance with the invention, the dried
catalyst obtained in step d) or the calcined catalyst obtained in
step e) advantageously undergoes a reduction treatment, for example
with hydrogen, pure or diluted, at high temperature. This treatment
can be used to activate said catalyst and form particles of
metallic cobalt in a zero-valent state. The temperature of this
reduction treatment is preferably in the range 200.degree. C. to
500.degree. C., and its duration is in the range 2 to 20 hours.
This reduction treatment is carried out either in situ (in the same
reactor as that in which the Fischer-Tropsch reaction in accordance
with the process of the invention is operated), or ex situ before
being charged into the reactor.
Fischer-Tropsch Process
Finally, another aim of the invention is the use of the catalyst in
accordance with the invention in a Fischer-Tropsch synthesis
process.
The Fischer-Tropsch process in accordance with the invention
results in the production of essentially linear and saturated C5+
hydrocarbons (containing at least 5 carbon atoms per molecule). The
hydrocarbons produced by the process of the invention are thus
essentially paraffinic hydrocarbons, wherein the fraction with the
highest boiling points may be converted into middle distillates
(gas oil cuts and kerosene) with a high yield, by a hydroconversion
process such as catalytic hydrocracking and/or
hydroisomerization.
The feed used to carry out the process of the invention comprises
synthesis gas. Synthesis gas is a mixture primarily comprising
carbon monoxide and hydrogen with H.sub.2/CO molar ratios which can
vary between a ratio of 0.5 and 4 depending on the process via
which it has been obtained. The H.sub.2/CO molar ratio of synthesis
gas is generally close to 3 when the synthesis gas is obtained from
a process for steam reforming hydrocarbons or alcohol. The
H.sub.2/CO molar ratio of synthesis gas is of the order of 1.5 to 2
when the synthesis gas is obtained from a partial oxidation
process. The H.sub.2/CO molar ratio of synthesis gas is generally
close to 2.5 when it is obtained from a thermal reforming process.
The H.sub.2/CO molar ratio of synthesis gas is generally close to 1
when it is obtained from a process for gasification and reforming
of CO.sub.2.
The catalyst used in the process for the synthesis of hydrocarbons
in accordance with the invention may be deployed in various types
of reactors, for example in a fixed bed, in a moving bed, in an
ebullated bed, or in fact in a three-phase fluidized bed. The use
of a catalyst in suspension in a three-phase fluidized bed,
preferably of a bubble column type, is preferred. In this preferred
embodiment of the catalyst, said catalyst is divided into a very
fine powder, particularly of the order of a few tens of microns;
this powder forms a suspension with the reaction medium. This
technology is also known to the person skilled in the art by the
terminology "slurry" process.
The hydrocarbon synthesis process in accordance with the invention
is operated at a total pressure in the range 0.1 to 15 MPa,
preferably in the range 0.5 to 10 MPa, at a temperature in the
range 150.degree. C. to 350.degree. C., preferably in the range
180.degree. C. to 270.degree. C. The hourly space velocity is
advantageously in the range 100 to 20000 volumes of synthesis gas
per volume of catalyst per hour (100 to 20000 h.sup.-1) and
preferably in the range 400 to 10000 volumes of synthesis gas per
volume of catalyst and per hour (400 to 10000 h.sup.-1).
The following examples demonstrate the gains in performances for
the catalysts in accordance with the invention.
EXAMPLES
Example 1 (Comparative): Catalyst a with Formula
Co/Al.sub.2O.sub.3
A catalyst A comprising cobalt deposited on an alumina support was
prepared by dry impregnation of an aqueous solution of cobalt
nitrate in order to deposit of the order of 10% by weight of Co in
two successive steps onto a gamma alumina powder (PURALOX.RTM. SCCa
5/170, SASOL) with a mean granulometry equal to 80 .mu.m, with a
surface area of 165 m.sup.2/g and with a pore volume, measured
using the nitrogen adsorption isotherm, of 0.4 mL/g.
After a first dry impregnation, the solid was dried in a flushed
bed at 120.degree. C. for 3 h in air, then calcined at 400.degree.
C. for 4 h in a flushed bed in a stream of air. The intermediate
catalyst contained approximately 6% by weight of Co. It underwent a
second dry impregnation step using a cobalt nitrate solution. The
solid obtained was dried in a flushed bed at 120.degree. C. for 3 h
in air, then calcined at 400.degree. C. for 4 h in a flushed bed in
a stream of air. The final catalyst A was obtained which contained
10.5% by weight of Co (in the form of the oxide,
Co.sub.3O.sub.4).
Example 2 (Comparative): Catalyst B with Formula
Co/Al.sub.2O.sub.3.SiO.sub.2
A catalyst B comprising cobalt deposited on a silica-alumina
support was prepared by dry impregnation of an aqueous solution of
cobalt nitrate so as to deposit, in one step, approximately 10% by
weight of Co onto a silica-alumina initially containing 5% by
weight of SiO.sub.2 and with a specific surface area of 180
m.sup.2/g and a pore volume of 0.8 mL/g
After dry impregnation, the solid was dried in a flushed bed at
120.degree. C. for 3 h in air, then calcined at 400.degree. C. for
4 h in a flushed bed. The final catalyst B was obtained which
contained 9.9% by weight of Co (in the form of the oxide,
Co.sub.3O.sub.4).
Example 3 (Comparative): Catalyst C with Formula
Co/CoAl.sub.2O.sub.4--Al.sub.2O.sub.3.SiO.sub.2
A catalyst C comprising cobalt deposited on a support, based on a
mixed oxide phase (in the form of spinel) included in a
silica-alumina, was prepared by dry impregnation of an aqueous
solution of cobalt nitrate, so as to deposit approximately 10% by
weight of cobalt onto the support in one step.
The spinel present in the support for catalyst C was a simple
spinel formed by cobalt aluminate, which was included in a
silica-alumina containing 5% by weight of SiO.sub.2, and had a
specific surface area of 180 m.sup.2/g and a pore volume of 0.8
mL/g. The spinel included in the silica-alumina was prepared by dry
impregnation of an aqueous solution of cobalt nitrate in a manner
such as to introduce 5% by weight of Co into said silica-alumina.
After drying at 120.degree. C. for 3 hours, the solid was calcined
at 850.degree. C. for 4 hours in air. The support for the catalyst,
denoted C', was formed by 5% by weight of cobalt in the form of
cobalt aluminate (i.e. 15% by weight of spinel) in
silica-alumina.
The active phase based on cobalt was then deposited onto said
support in one step, by dry impregnation, in accordance with a
protocol identical to that described for the preparation of
catalyst B. The steps of calcining and drying were also carried out
under the operating conditions described for Example 2. The
concentration of cobalt in the cobalt nitrate solution used for the
successive impregnations was selected in order to obtain the
catalyst C with the desired final Co content.
The final catalyst C had a total cobalt content of 15.7% by weight
(the Co content present in the spinel phase being included) and a
cobalt content in the form of the oxide, Co.sub.3O.sub.4, of 10.7%
by weight.
Example 4 (Comparative): Catalyst D with Formula
Co/CoAl.sub.2O.sub.4--Al.sub.2O.sub.3.SiO.sub.2 Containing Acetic
Acid
A catalyst D comprising cobalt and acetic acid deposited on a
support, based on a spinel included in a silica-alumina, was
prepared by dry impregnation of an aqueous solution of cobalt
nitrate then a solution of acetic acid so as to deposit
approximately 10% by weight of cobalt onto the support.
The active phase based on cobalt was deposited onto the support C'
from Example 3 in one step, by dry impregnation of a solution
containing cobalt nitrate After dry impregnation, the solid
underwent drying in a flushed bed at 120.degree. C. for 3 h in
air.
In a second step, acetic acid was deposited onto the above solid in
one step, by dry impregnation of a solution containing acetic acid
(Sigma Aldrich.RTM., >99%) at a concentration which could obtain
an acetic acid:Co molar ratio on the final catalyst of 0.2. After
dry impregnation, the solid underwent a maturation in an atmosphere
saturated with water for 9 hours at ambient temperature, then was
dried in a flushed bed at 120.degree. C. for 3 h in air, then
treated for 4 h in a flushed bed under nitrogen at 400.degree.
C.
The final catalyst D had a total cobalt content of 14.6% by weight
(the Co content present in the spinel phase being included) and a
cobalt content in the form of the oxide, Co.sub.3O.sub.4, of 9.6%
by weight.
Example 5 (Comparative): Catalyst E with Formula
Co/CoAl.sub.2O.sub.4--Al.sub.2O.sub.3.SiO.sub.2 Containing Citric
Acid
A catalyst E comprising cobalt and citric acid deposited on a
support, based on a spinel included in a silica-alumina, was
prepared by dry impregnation of an aqueous solution of cobalt
nitrate, then of an aqueous citric acid solution, so as to deposit
approximately 10% by weight of cobalt onto the support.
The active phase based on cobalt was deposited onto the support C'
from Example 3 in one step, by dry impregnation of a solution
containing cobalt nitrate. After dry impregnation, the solid
underwent drying in a flushed bed at 120.degree. C. for 3 h in
air.
In a second step, citric acid was deposited onto the above solid in
one step, by dry impregnation of a solution containing citric acid
(Sigma Aldrich.RTM., >99%) at a concentration which could obtain
a citric acid:Co molar ratio on the final catalyst of 0.5. After
dry impregnation, the solid underwent a maturation in an atmosphere
saturated with water for 9 hours at ambient temperature, then was
dried in a flushed bed at 120.degree. C. for 3 h in air, then
treated for 4 h in a flushed bed under nitrogen at 400.degree.
C.
The final catalyst E had a total cobalt content of 14.0% by weight
(the Co content present in the spinel phase being included) and a
cobalt content in the form of the oxide, Co.sub.3O.sub.4, of 9.0%
by weight.
Example 6 (in Accordance with the Invention): Catalyst F with
Formula Co/CoAl.sub.2O.sub.4--Al.sub.2O.sub.3.SiO.sub.2 Containing
Malonic Acid
A catalyst F comprising cobalt and malonic acid deposited on a
support, based on a spinel included in a silica-alumina, was
prepared by dry impregnation of an aqueous solution of cobalt
nitrate, then of an ethanolic malonic acid solution, so as to
deposit approximately 10% by weight of cobalt onto the support.
The active phase based on cobalt was deposited onto the support C'
from Example 3 in one step, by dry impregnation of a solution
containing cobalt nitrate. After dry impregnation, the solid
underwent drying in a flushed bed at 120.degree. C. for 3 h in
air.
In a second step, malonic acid was deposited onto the above solid
in one step, by dry impregnation of an ethanolic solution
containing malonic acid (Sigma Aldrich.RTM., >98%) at a
concentration which could obtain a malonic acid:Co molar ratio on
the final catalyst of 0.2. After dry impregnation, the solid
underwent a maturation in an atmosphere saturated with water for 9
hours at ambient temperature, then was dried in a flushed bed at
120.degree. C. for 3 h in air, then treated for 4 h in a flushed
bed under nitrogen at 400.degree. C.
The final catalyst F had a total cobalt content of 15.1% by weight
(the Co content present in the spinel phase being included) and a
cobalt content in the form of the oxide, Co.sub.3O.sub.4, of 10.1%
by weight.
Example 7 (in Accordance with the Invention): Catalyst G with
Formula Co/CoAl.sub.2O.sub.4--Al.sub.2O.sub.3.SiO.sub.2 Containing
Succinic Acid
A catalyst H comprising cobalt and succinic acid deposited on a
support, based on a spinel included in a silica-alumina, was
prepared by dry impregnation of an aqueous solution of cobalt
nitrate, then of an ethanolic succinic acid solution, so as to
deposit approximately 10% by weight of cobalt onto the support.
The active phase based on cobalt was deposited onto the support C'
from Example 3 in one step, by dry impregnation of a solution
containing cobalt nitrate. After dry impregnation, the solid
underwent drying in a flushed bed at 120.degree. C. for 3 h in
air.
In a second step, succinic acid was deposited onto the above solid
in one step, by dry impregnation of an ethanolic solution
containing succinic acid (Sigma Aldrich.RTM., >98%) at a
concentration which could obtain a succinic acid:Co molar ratio on
the final catalyst of 0.2. After dry impregnation, the solid
underwent a maturation in an atmosphere saturated with water for 9
hours at ambient temperature, then was dried in a flushed bed at
120.degree. C. for 3 h in air, then treated for 4 h in a flushed
bed under nitrogen at 400.degree. C.
The final catalyst G had a total cobalt content of 14.8% by weight
(the Co content present in the spinel phase being included) and a
cobalt content in the form of the oxide, Co.sub.3O.sub.4, of 9.8%
by weight.
Example 8 (in Accordance with the Invention): Catalyst H with
Formula Co/CoAl.sub.2O.sub.4--Al.sub.2O.sub.3SiO.sub.2 Containing
Succinic Acid
Catalyst H was prepared in a manner similar to that for catalyst G,
with the exception that it did not undergo heat treatment under
nitrogen at 400.degree. C. at the end of the preparation.
Example 9: Catalytic Performances of Catalysts a to H in the
Fischer-Tropsch Reaction
Before being tested using the Fischer-Tropsch synthesis, the
catalysts A, B, C, D, E, F, G and H were reduced in situ at
400.degree. C. in a stream of pure hydrogen for 16 hours. The
Fischer-Tropsch synthesis reaction was operated in a fixed bed type
tube reactor which was operated continuously.
Each of the catalysts was in the form of a powder with a diameter
in the range 40 and 150 microns.
The test conditions were as follows: temperature=216.degree. C.
total pressure=2 MPa hourly space velocity (HSV)=4100
NL/h.sup.-1/kg.sub.catalyst H.sub.2/CO molar ratio=2/1
The results, expressed in terms of activity (CO conversion, as a %)
and selectivity (percentage by weight of C.sub.8.sup.+ hydrocarbons
over the total of the products formed), are shown in Table 1.
TABLE-US-00001 TABLE 1 Catalytic performances for each catalyst
Conversion of C.sub.8.sup.+ selectivity at CO at 70 h in 70 h in
reaction reaction stream stream Catalyst (%) (% by weight) A
(comparative) 27.5 57.1 B (comparative) 38.1 65.9 C (comparative)
44.7 68.0 D (comparative) 35.3 62.0 E (comparative) 41.3 56.1 F
(invention) 51.3 70.1 G (invention) 53.5 70.5 H (invention) 53.2
70.6
The results shown in Table 1 demonstrate that the catalysts in
accordance with the invention are more active and/or more selective
than the catalysts known in the prior art.
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